Yes, change the ATF at operating temperature. This has two advantages over changing it cold:
1. Drains out more particles suspended in the fluid.
2. Less chance of overfilling since the fluid remaining after the drain is already thermally expanded.
Yes, you can do it that way. Once the level is between the dots, add just a small amount at a time so to not overfill it.
Another method is to measure the amount drained out then replace the same amount. (That's how I do it, but I found that measuring into the bottle is inaccurate. So I bought a measuring cylinder to get the amount right.) Make sure the level is good before you drain the old fluid.
I don't think it's necessary to make a special trip after changing the fluid. However, check it again after returning from your first trip. Make sure the level is at or near the upper dot - not above. I find that the fluid level doesn't change from heating up the new 3.5 quarts. Also, check the drain bolt for any sign of leaking.
Dave